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Conformal Coating Immersable in Water



Conformal Coating Immersable in Water | 16 May, 2001

I am looking for a conformal coating to protect a PWB that will be completely submerged in water. Unfortunately polyurethane will not work because it will not fill all of the small spaces and leaves voids.

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Conformal Coating Immersable in Water | 16 May, 2001

Urethane and parylene have the best long term humidity resistance of the conformal coatings. Since yer not hep about urethane, try the parylene [,,,, etc]. It will absorb less than 0.1%. And since they are vapor deposited, parylenes are noted for their ability to penetrate small spaces, probably overcoming the voiding limitation you see in urethanes. On the other hand, the process will give you incentive to get it correct the first time. [Ummm, now that sounds scary!!!] Yer gunna need a chain saw to cut through the stuff!!!

What�s your thinking on encapsulation as an alternative to parylene and still attaining a less-hermetic conformal coating? [It�s something to consider, because in real life, it�s going tough to distinguish a parylene from encapsulation.] Master Bond [and probably others] has a reworkable encapsulant. Beyond that, I know nothing about it. [Just got the flyer tonight.]

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Conformal Coating Immersable in Water | 17 May, 2001

Parylene is arguable the best conformal coating there is, unfortunately it's also the most expensive. We had considered using it some time back, but due to environmental and safety issues, we would have had to build a new building to house the process (we are a high volume manufacturer).

We run a salt water immersion test on some of our modules. They have to be functional during immersion in salt water (1 hour test). All of our modules requiring this test are potted. We only use conformal coating on boards that will not be exposed to the possibility of immersion.

We use silicones for both conformal coatings and potting. They have higher temperature capabilities, low modulus, and are easy to repair.

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